An embryonic battle of the sexes

New insight on a crucial step in fertilization

It’s common scientific knowledge that all organisms inherit their mitochondria—the cell’s “power plants”—from their mothers.

But what happens to all the father’s mitochondria? How and why paternal mitochondria are prevented from getting passed onto their offspring after fertilization has been a mystery.

Now, Dr. Eli Arama of the Department of Molecular Genetics and his team have discovered special cellular vesicles that originate in the female fruit flies’ egg and which actively seek out and destroy the father’s mitochondria upon fertilization. The study, recently published in Development Cell, may help shed light on the prevailing theories.

In contrast to the existing theories, one of which describes a process in which the paternal mitochondria passively disappear, Dr. Arama’s findings show a more turbulent process - call it the first love-hate relationship. He and his lab members found that as soon as the sperm enters the egg, the cellular vesicles in the egg (of a fruit fly, in this case) immediately are attracted to the sperm like a magnet. They then proceed to disintegrate the sperm’s outer membrane and separate the mitochondria from the tail section, which is subsequently cut into smaller pieces that are then devoured by a system of “self-eating” called autophagy.

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Dr. Arama is an expert in cellular destruction processes. Upon close observation, he found that these violent vesicles did not resemble those typically involved in autophagy. They were too large and differently shaped. What they had come across were entirely distinct structures.

The discovery, which the team believes is relevant for other organisms with flagellated sperm - including humans - may lead to an understanding of some of the IVF-associated pregnancy miscarriages. It may be that this invasive procedure somehow abrogates the ability of the egg to destroy the paternal mitochondria. Dr. Arama and his team hope that further research will help shed new light on a variety of issues pertaining to paternal mitochondria, with an ultimate goal of understanding mitochondrial turnover and fertility.

Dr. Arama is supported by the Yeda-Sela Center for Basic Research, the Fritz Thyssen Stiftung, and the estate of Rudolfine Steindling. He is the incumbent of the Corinne S. Koshland Career Development Chair.